feat: Move SimpleShowMaskRPT from niworkflows

[effigies]

sdcflows uses this interface but is producing warnings that niworkflows reporting has been moved to nireports. Making that more true.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.69%. Comparing base (6404af3) to head (59cb904).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #135      +/-   ##
==========================================
+ Coverage   60.34%   66.69%   +6.34%     
==========================================
  Files          20       21       +1     
  Lines        2242     2255      +13     
  Branches      399      399              
==========================================
+ Hits         1353     1504     +151     
+ Misses        795      643     -152     
- Partials       94      108      +14     

Flag	Coverage Δ
unittests	66.54% <100.00%> (?)

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[effigies]

This is already done in #71. I've rebased that and will merge if it tests clean.